Production of deoxidated,depurated,killed and refined steels using aluminum-lithium alloys

ABSTRACT

THE INVENTION RELATES TO THE USE OF ALLOYS CONSISTING ESSENTIALLY OF ALUMINUM-LITHIUM FOR THE PURPOSE OR DEOXIDIZING, DEPURATING, KILLING AND REFINING ANY KIND OR CARBON- OR ALLOY-STEEL. THE ALLOYS USED IN THE PROCESS OF THE INVENTION CONTAIN FROM 50 TO 99.7% OF ALUMINUM AND FROM 0.3 TO 8% OF LITHIUM: THEY MAY ALSO SUITABLY CONTAIN AT LEAST ONE ELEMENT SELCTED FROM THE GROUP CONSISTING FO RARE EARTHS (TR), CA, BA, FE AND B, IN PERCENTAGE RANGES AS FOLLOWS: FE 0.5-20%; TR 0.5-13%; CA 0.2-8%; BA 0.2-2%.

3,795,505 PRODUCTION OF DEOXIDATED, DEPURATED, KILLED AND REFLNED STEELS USDIG ALUMINUM-LITHIUM ALLOYS Dante Corradini, Via Cacciolepori 11, Milan, Italy No Drawing. Continuation-impart of application Ser. No. 145,049, May 19, 1971, which is a continuation of application Ser. No. 633,714, Apr. 26, 1967, both now abandoned. This application Oct. 18, 1971, Ser. No. 190,402

Claims priority, application Italy, Apr. 7, 1967, 14,703/67 Int. Cl. C21c 7/08 US. Cl. 75-53 1 Claim ABSTRACT OF THE DISCLOSURE The invention relates to the use of alloys consisting essentially of aluminum-lithium for the purpose of deoxldizing, depurating, killing and refining any kind of carbonor alloy-steel.

, The alloys used in the process of the invention contain from 50 to 99.7% of aluminum and from 0.3 to 8% of lithium; they may also suitably contain at least one element selected from the group consisting of rare earths (TR), Ca, Ba, Fe and B, in percentage ranges as follows:

Fe 05-20%; TR 05-13%; Ca -0.2-8%; Ba 0.22%.

This application is a continuation-in-part of copending application Ser. No. 145,049 filed May 19, 1971, now abandoned, which in turn is a streamlined continuation of application Ser. No. 633,714 filed Apr. 26, 1967, now abandoned.

The present invention relates to alloys consisting of or comprising aluminium-lithium for the purpose of deoxidizing, depurating, killing and refining low, high and medium carbon steels, and also alloy-steels. The invention provides also the method for the production of such steels deoxidated, depurated, killed and refined by the above mentioned alloys, which greatly improve their physicalmechanical characteristics.

More particularly the present invention relates to aluminium-alloys which comprise from 50 to 99.7% of aluminium and from 0.3 to 8% of lithium. All percentage referred in the present application are by weight.

As it is well known, the most detrimental non-metallic impurities contained in the steels, at the elementary or combined state, are: oxygen, hydrogen, nitrogen and sulphur.

For a long time aluminium has been employed to deoxidate, kill and refine steels, but it produces alumina inclusions and forms aluminium nitride which may impart poor engineering properties to the steel. Moreover the aluminium seems to influence the distribution and the type of the metal sulfide inclusions and, depending on the quantity of aluminium added to the liquid steel, the sulfide inclusions may assume such distributions which are highly harmful to the characteristics of the steels.

Aluminum alloys, containing from up to 95% of various metals including lithium, for depurating steel were proposed in an English patent of 1902.

Later on in 1927, in an American patent relating to structural Al-Li alloys it is aflirmed that similar alloys, proposed for depurating steel, are unsuitable for structural alloys, because they contain more than 40% of lithium.

Notwithstanding these antecedents, or perhaps owing to these antecedents Li-Al alloys were afterwards no more considered for depurating molten steel, as can be drawn e.g. from the Revue de Metallurgie, 1963, where methods for adding metal lithium to molten steel are considered and where it is concluded that such methods-often asso- United States Patent 6 ciated with argon bubbling through the molten steelare unsatisfactory because of explosion danger and because only a small percentage of the added lithium is utilized while the greatest part is lost through evaporation; the boiling point of Li being of 1325 C.

However, it was confirmed that lithium additions to molten steel can notably improve its mechanical characteristics, in that it lowers the oxygen, nitrogen, hydrogen and sulphur content of the steel, it allows a reduction of inclusions and exerts a grain refining action.

On the other hand it was within the prior art knowledge that lithium reacts with the moisture in the air, which reaction of course must be avoided in order not to introduce hydrogen and oxygen in the steel with the lithium addition.

It was also known that liquid lithium will react with virtually every other material including refractories and that lithium oxide has a quite remarkable solvent action on almost all known refractory materials, which may therefore pollute the steel.

There are also known for the treatment of steel, aluminium-rare earths alloys (the term rare earths, TR, issued to mean a mixture of metals of the lanthanides group, commercially named Mischmetal which contains approximately: cerium 46-52%, lanthanium 24-27%, neodyum 14-18% the remaining material being constituted by other elements of the rare earth group).

However, although these alloys represent a certain progress when compared with the use of pure aluminium, they do not solve the inclusions problem as the rare earths do in no way react with the formed A1 0 in order to eliminate it; moreover the rare earth oxides and sulfides formed by reaction with oxygen and sulphur, remain in the steel.

This being the situation of the prior art I endeavoured to find a way of introducing lithium in molten steel avoiding the inconveniences above reported.

In so far as the binary alloys Al-Li are concerned, I have found that if the content of Li is of about 0.3% 01' less, the alloy will practically act as if composed by pure Al.

I have also found that Al-Li alloys are stable in usual storage conditions, that is in contact with the atmosphere, only if the Li content is lower than 1.2%

Further I have found that it is possible to prepare Al-Li Alloys, stable to storage and with a Li content higher than 1.2% by addition to the Al-Li alloy of at least one of the following elements in the indicated percentages Percent Ca 0.2-8 TR 0.5-13 Fe 0.5-20 Ba 0.2-2

Further I have found that also in the thug stabilized alloys, the Li content may not be higher than 8%, otherwise when adding the alloy to the ladle it may cause dangerous molten steel projection, refractories corrosions, contamination of the steel by A1 0 inclusions, etc. For example, a Al-Li-Fe alloy having 8% of Li, 10% of Fe and 82% of Al, is a quite stable one.

I have further found that the addition of TR, Ca, Ba, to the Al-Li alloys of the invention, within the given limits, provide the following advantages:

2. much better elimination of the impurities 0 N S, H and of the A1 0 inclusions and prevention of AlN formation;

a much better killing and refining action;

a higher yield of the alloy components;

a practically total elimination of the refractory etching.

One portion of rare earths added to the new alloys hereabove described correspond, for the purpose of the present invention, approximately 0.5 parts of cerium or to 0.2 parts of lanthanum.

Furthermore I have found that by adding from 0.2 to 1.7% of boron to the ternary alloys Al-Li-TR, it is possible to introduce this element into the steel without boron nitride formation (which causes steel embrittlement) thus achieving, besides the advantages hereabove specified, higher and constant boron yields, much superior to those usually obtained employing the known boronalloys manufactured for such purpose.

Various other elements may be added to the alloys of the present invention such as: Si, Mn, Ni, Ti, Zr, Fe, Y, Mg. Depending on the element used, either an economic advantage may be obtained or a special steel endowed with peculiar characteristics.

In any case, in order to attain the principal object of the present invention, the alloys must have an A1 content higher than 50%, the lithium content being always comprised bewteen 0.3 and 8%. In order to demonstrate that the following percentages of Li: 0.3, 1.2 and 8%, in the Al alloys are critical, experiments A, B, C were carried out. In Example I, II and III the performances of steels treated with the alloys of the invention are reported.

In experiments A, B and C, the amount of alloy additioned was always kept in the range of 1%., by weight of the steel.

EXPERIMENTS A Al-Li alloy containing 0.35% of Li was used with a steel of the following composition: C 0.18%-Mn 0.84%Si 0.32%P+S 0.06%.

Microprobe analysis of the steel inclusions, gave the following results: total inclusions 197 p.p.m., FeO 16%; A1 34%; Si0 36%; MnO 6%; others 8%. By using the same percentage, namely 1%.], of pure aluminum, the following results were obtained: total inclusions 195 p.p.m., FeO A1 0 35%; SiO 34%; MnO 7%, others 9%. The amount of inclusions does not practically differ in the two cases.

The reported results each of which represent the weighted mean of five experiments, clearly show that an Al-Li alloy with 0.35% of Li has practically no effect on the steel.

EXPERIMENTS B Al-Li alloys containing 1, 1.2, 1.5% of Li were stored for 1 year. After this storage time the initial color of the alloy with 1.5 of Li had changed from pale grey to dark grey and the surface of this alloy presented a few scales which were removed with a steel brush before using the alloy.

The same steel and technique as in Experiment A were used throughout.

With pure A1: total inclusions 195 ppm; FeO 15% A1 0 35%; SiO, 34%; MnO 7%, others 9%.

Alloy Al-Li with 1% Li: total inclusions 107 p.p.m.; FeO 7.4%; A1 0 16%; SiO 32%; MnO 22%; others 22.6%.

Alloy Al-Li with 1.2% Li: total inclusions 103 p.p.m.; FeO 9.4%; A1 0 15.6%; SiO 30%; MnO 22%; others 23%.

Alloy Al-Li with 1.5% Li: total inclusions 91 p.p.m.; FeO 9%; A1 0 15%; SiO MnO 25%; others 20%.

EXPERIMENTS C The following alloys were used, compositions inpercentage,

A? number:

Hereinafter is reported on the experiments made with some of these alloys.

A ladle, coated with aluminous refractories, of 600 1. capacity was used in the experiments.

The temperature of the molten steel was in the range of 1590 C.-l630 C. The same steel and technique were used throughout. Li-Al-Ca alloys with pure Al, total inclusions p.p.m. 187, FeO 18%,

A1 0 31%, SiO 30%, MnO 9%, others 12% with alloy No. 6, total inclusions p.p.m. 160, FeO 14%, A1 0 26%,. SiO 25%, MnO 17%, others 18% with alloy No. 8, very strong agitation of the molten steel, total inclusions p.p.m. 191, FeO 17%, A1 0 33%, SiO 30%, MnO 10%, others 10% with alloy No. 10 the operation resulted dangerous because too violent agitation of the molten steel occurred. Li-Al-TR alloys with alloy No. 1 total inclusions p.p.m. 146, FeO 11%, A1 0 26%, SiO 28%, MnO 15%, others 20% with alloy No. 2 total inclusions p.p.m. 152, FeO 9%, Al O 30%, SiO 28%, MnO 17%, others 16% with alloy No. 5, same as alloy No. 10

The hereinafter listed alloys, from c onwards (not considering aluminum metal, named a, and alloy b, only used for comparative purposes), which are mentioned only as illustrative but not as limitative of the invention, have been successfully applied:

Particularly good results have been obtained with the following standard alloys: s, m, n, d and 1.

All the alloys of the present invention may be employed for the production of low, medium and high carbon steels, and also for the production of low, medium and high alloy steels as for example stainless steel, chrome and manganese steels.

The addition percentage of these alloys to the steel may vary depending on the steel-type treated and also on the employment field which the steel is destined to. In any case these additions are limited as follows: from 0.01 to 0.16%, i.e. from grs. to 1600 grs. per ton of liquid steel.

According to a preferred method the new alloys are added to the steel by plunging it down to the bottom of the filled ladle; alternatively the alloy may be introduced at the bottom of the ladle where thereafter the molten steel is poured.

Following these methods, the alloy uniformly reacts with all the liquid mass.

It is also possible to add the alloy in the furnace or in the ingot moul, in shapes such as stars, pellets, wires, etc.

The present invention may be successfully used in all those fields of metallurgical industry wherein Al has been used up to date to kill and refine steel, as well as to control its grain size to obtain higher purity qualities.

The invention is hereafter illustrated by the examples in which, for comparison purposes, the same steel are treated with A1 alone and with alloys, consisting of or comprising Al-Li. All percentages are by weight.

The invention is hereafter illustrated by the following examples in which for comparison purposes the same steel was treated: with aluminum alone, Al 90% +TR 10%, and with Type A and C alloys of the invention. All

percentages are by welght' Elonga- Reduc- Resilience Alloy Tension tion, tion of (CharpY). Example 1 number strength percent area kg./cm.

Trglalrted o The following steels. glfig a 33;, m 2 am 2.7 Type I: c 0.24Mn 0.72-Si 0.26-P 0.024 0.03 S Type II: C 0.32-Mn 1.60Si 0.25-P 0.02S 0.03 Type of inclusions according to ASTM 45/63 Type III C 0.42Mn- 0.75--Si 0.25P 0.015S 0.03 AHOY number A B G D E treated in the molten state as 1nd1cated, thereafter normal- Treated with ized at 850 C. and tempered at 530 C., gave the fol- 13- a egg a- 2 g i 1 lowing results a S Tension Yield Elonga- Reduction Resilience Treated Alloy strength strength, tion, of area, Charpy, withnumber kgJmmJ kg./mm. percent percent kg./rn./cm.

Type I steel AI a, 53.20 30.70 30.00 51.20 4.95 .Al-TR b 53.25 30 .80 30.60 53 .40 5.80 Al-Li-TR 11 53.25 31.40 31.40 56.30 6.74

Type II steel a 65.20 44.50 27.2 55.00 6.32 .Al-TR b 65.60 44.60 27.8 56.70 6.48 Al-Li-TR 11 66.20 44.95 23.6 60 .50 7.30

Type III steel Al a 65.6 39.10 24.2 37.5 2.54 Al-TR b 65.7 40.20 25.1 39 .4 2.81 AI-Li-TR n 66.3 41.60 27.8 .6 3.42

Analysis of the steels as above treated, made according to ASTM 45/63 test method gave the following type of 4 Al-Li-TR b 2 Example 2 A 12/14 manganese steel was treated in the molten state as follows, then austenized at 1100" C. and mill hammer casted therewith.

6 Analysis according to ASTM 45/ 63 gave the following types of inclusions:

Mn 0.72; Si 0.28; S 0.02; P 0.016 was treated in the molten state as follows: thereafter normalized at 850 C. and tempered at 530 C. The following results were obtained:

Only from an interpretative point of view, which is in no way limitative upon the above disclosed invention, it may be thought that the highly advantageous results obtained with the peculiar Al-Li alloys of the present invention derive from an action both chemical and physical of Li. As a matter of fact it seems that this metal has a high reaction rate towards the oxygen present in the steel so forming the loW-density-lithium oxide which further reacts with A1 0 and with the other oxides of refractory character present in the steel leading to lowmelting complex products which easily coagulate and decant gathering in the slag.

Moreover Li when coming. into contact with molten steel, evaporates, thus exerting a strong action on the bath i.e. of bubbling and dragging the impurities into the slag.

Of course, the exploitation of these so advantageous characteristics of Li is rendered possibly by the fact that I use it only in critically limited amounts, diluted into the active Al, and also by the fact that I have found the manner to stabilize the Al-Li alloys containing from 1.2 to

8% of Li.

It has been impossible up to now to fully understand the stabilizing action exerted on the Al-Li alloys by the elements Fe, Ba, Ca, TR.

However such a circumstance is of no consequence for the purposes of the invention.

What is claimed is:

1. In the method of deoxidizing, depurating, killing and refining steels by adding aluminum alloys to the molten steel, the improvement consisting of using as said aluminum alloy an alloy consisting of more than 98.8% to 99.7% aluminum and 0.3% to less than 1.2% lithium in an amount of 0.0 10.16% based on the weight ofthe steel.

References Cited UNITED STATES PATENTS 2,233,726 3/ 1941 Belding 7558 2,360,717 10/ 1944 Phelps 7558 X 2,609,289 9/ 1952 McKinney et a1. 7558 X 2,683,661 7/1954 Tisdale et a1. 7558 X 2,705,196 3/1955 Wever et a1 7558 Jordan 7558 X Pierce 75-58 Henke 7558 Bieniosek 7558 X Knapp et a1. 7558 X Volianik 7558 X Loomis 7558 Arnaud 7558 X Lynch 7558 X Behrens et a1. 7558 X Spengler et a1 7558 X Czochralski et a1 7S---138 Great Britain.

L. DEWAYNE RUTLEDGE, Primary Examiner P. D. ROSENBERG, Assistant Examiner US. Cl. X.R. 

